Fluid motors are preferably driven with pressurized air or with hydraulic liquid. The work done by the pressure medium during its expansion is used for driving.
A well-known type of motor is the vane motor. It comprises a rotor rotating in a motor chamber with radial vanes. When the rotor is rotated the spaces largely sealed by the vanes and the side wall of the motor chamber change in volume. The pressure medium introduced into these spaces expands and thus drives the rotor.
Such motors have proved very reliable for a great variety of applications, such as for use in hoisting apparatus. For many applications, a braking unit is necessary for braking and holding fast the vane rotor when no pressure medium is supplied. In particular in use in hoisting apparatus, the load is thereby prevented from falling down.
While the braking unit may be coupled to the motor via a shaft in a great variety of well-known hoisting apparatus, it is a separate part external to the motor chamber, i.e., outside of the chamber in which the pressure medium expands.
EP 1 099 040 discloses a vane motor driven by pressurized air. A vane rotor is excentrically rotatably supported in a cylindrical motor sleeve. The motor is driven by introducing pressurized air which expands as the chambers formed between the vanes get larger. A separate braking unit is provided at a shaft of the motor. To lubricate the motor, the vane rotor has longitudinal bores filled with a lubricating agent having a pasty consistency.
DE 1 102 488 discloses a vane motor for hoisting apparatus having a drive shaft which is fixedly braked by a friction brake when the pressurized air is switched off or fails. For this purpose, there is a braking disc on a motor shaft end, which has a centrally arranged pressure cylinder and is pressed against a wear ring of the motor housing by means of a spring load. The pressurized air introduced via an inlet is supplied to a pressure cylinder of the brake disc, causing it to lift off from the wear ring against the resistance of the springs and thus enables the operation of the motor.
WO 95/02762 shows a hydraulic motor. A rotor rotates in a motor chamber. The rotor is axially moveable and is pressed by springs with a conical section against a friction surface fixed with respect to the housing. The motor chamber is in communication with the conical friction pair via channels having valves arranged therein. In operation, the pressure medium passes from the motor chamber to the friction pair and causes axial displacement of the rotor which leads to the friction pair being separated and thus to the brake being released.
WO 97/02406 of the applicant shows a vane rotor with an integrated braking unit. A vane rotor is drivable in a motor chamber by means of pressurized air. A braking element is displaceable and loaded by springs and arranged axially directly adjacent to the vane rotor. The vane rotor thus forms a friction pair at its end face together with the braking element. The friction pair is arranged in the motor chamber, so that in operation the compressed air present therein acts on the braking element and displaces it against the spring load in such a way that the brake is released. This construction has been well-proven in practice. In particular, it results in a compact structure.
It is the object of the present invention to propose a motor in which the braking action is yet improved in a simple manner in comparison to prior-art constructions.
The object is achieved by a motor according to claim 1. Dependent claims refer to advantageous embodiments of the invention.